1. Field of the Invention
The present invention relates to a magneto-resistive effect (MR) element and a manufacturing method thereof, and particularly relates to a configuration of a spacer layer.
2. Description of the Related Art
Reproducing heads with high sensitivity and high output are in demand in conjunction with condensing of high recording density in hard disk drives (HDD). As an example of this type of reproducing head, a spin valve head has been developed. A spin valve head includes a nonmagnetic metal layer and a pair of ferromagnetic layers positioned on both sides of the nonmagnetic metal layer in a manner of contacting the nonmagnetic metal layer. The magnetization direction of one of the ferromagnetic layers is pinned in one direction (hereinafter, this type of layer is referred to as a magnetization pinned layer), and the magnetization direction of the other one of the ferromagnetic layers freely rotates in response to an external magnetic field (hereinafter, this type of layer is referred to as a magnetization free layer). When the external magnetic field is applied, the relative angle of the spins between the magnetization pinned layer and the magnetization free layer changes so that magneto-resistive change is realized. Typically, the magnetization direction of the magnetization pinned layer is pinned by utilizing exchange coupling force of an anti-ferromagnetic layer.
In the meantime, in order to realize further condensing of high recording density, a reduction of a read gap (a space between upper and lower shield layers) is required. However, when the read gap is reduced to approximately 20 nm, it is difficult to place an anti-ferromagnetic layer within the read gap. Therefore, a configuration has been developed in which a pair of magnetization free layers is arranged on both sides of a spacer layer. According to this configuration, reduction of the read gap is easily realized because no anti-ferromagnetic layer is required.
With either configuration, the spacer layer is a necessary component to realize the magneto-resistive change. Materials for the spacer layer that are promising for achieving a large magneto-resistive ratio (hereinafter referred to as MR ratio) have been developed. Conventionally, a technology has been known that an MR ratio is increased by disposing a resistance adjustment layer in a spacer layer and by narrowing a path where a sense current flows. However, since sense current is concentrated to a conductive part and thereby a current density is increased, this technology is not preferable from the view point of reliability. U.S. Patent Application Publication No. 2008/0062557 discloses a technology that an oxide semiconductor layer such as ZnO, TiO and the like is used as a part of a spacer layer. Since this technology allows to prevent a sense current from being concentrated, it is possible to increase the reliability while the MR ratio is increased.
The ferromagnetic layers adjacent to the spacer layer are normally composed of Co, Ni, Fe and the like as a primary component. When these elements are positioned in a manner of contacting the oxide semiconductor layer, the ferromagnetic layers may be oxidized by an oxidation action of oxygen contained in the oxide semiconductor layer. Thereby, polarizability may be decreased and the MR ratio may be lowered. U.S. Patent Application Publication No. 2008/0062557 further discloses a technology that a nonmagnetic metal layer composed of copper, gold, silver or the like is disposed between a ferromagnetic layer composed of CoFe and the like and an oxide semiconductor layer. It is expected that these nonmagnetic metal layers prevent diffusion of oxygen contained in the oxide semiconductor layer and oxidation of the ferromagnetic layer. However, with the nonmagnetic metal layers composed of copper, gold, silver or the like, sufficient antioxidant effects are often not obtained in particular when the diffusion of oxygen is likely to occur under a high temperature environment.
It is an object of the present invention to provide an MR element where oxidation of a magnetic layer adjacent to a spacer layer is prevented and in which a large MR ratio is realized.